diff --git a/Lib/importlib/_bootstrap.py b/Lib/importlib/_bootstrap.py
--- a/Lib/importlib/_bootstrap.py
+++ b/Lib/importlib/_bootstrap.py
@@ -33,7 +33,10 @@ def _make_relax_case():
     if sys.platform.startswith(_CASE_INSENSITIVE_PLATFORMS):
         def _relax_case():
             """True if filenames must be checked case-insensitively."""
-            return b'PYTHONCASEOK' in _os.environ
+            if sys.flags.ignore_environment:
+                return False
+            else:
+                return b'PYTHONCASEOK' in _os.environ
     else:
         def _relax_case():
             """True if filenames must be checked case-insensitively."""
diff --git a/Lib/test/test_importlib/extension/test_case_sensitivity.py b/Lib/test/test_importlib/extension/test_case_sensitivity.py
--- a/Lib/test/test_importlib/extension/test_case_sensitivity.py
+++ b/Lib/test/test_importlib/extension/test_case_sensitivity.py
@@ -35,7 +35,10 @@ class ExtensionModuleCaseSensitivityTest
                 self.skipTest('os.environ changes not reflected in '
                               '_os.environ')
             loader = self.find_module()
-            self.assertTrue(hasattr(loader, 'load_module'))
+            if sys.flags.ignore_environment:
+                self.assertIsNone(loader)
+            else:
+                self.assertTrue(hasattr(loader, 'load_module'))
 
 
 
diff --git a/Lib/test/test_importlib/source/test_case_sensitivity.py b/Lib/test/test_importlib/source/test_case_sensitivity.py
--- a/Lib/test/test_importlib/source/test_case_sensitivity.py
+++ b/Lib/test/test_importlib/source/test_case_sensitivity.py
@@ -58,8 +58,11 @@ class CaseSensitivityTest(unittest.TestC
             sensitive, insensitive = self.sensitivity_test()
             self.assertTrue(hasattr(sensitive, 'load_module'))
             self.assertIn(self.name, sensitive.get_filename(self.name))
-            self.assertTrue(hasattr(insensitive, 'load_module'))
-            self.assertIn(self.name, insensitive.get_filename(self.name))
+            if sys.flags.ignore_environment:
+                self.assertIsNone(insensitive)
+            else:
+                self.assertTrue(hasattr(insensitive, 'load_module'))
+                self.assertIn(self.name, insensitive.get_filename(self.name))
 
 
 def test_main():